Geometric series refers to a series in which the ratio of each term to its previous term is equal to the same constant from the second term, usually expressed by G and P. This constant is called the common ratio of geometric series, usually expressed by the letter Q (q≠0), and geometric series a 1≠ 0. Where each item in {an} is not 0. Note: When q= 1, an is a constant series.

Among integers, numbers that are not divisible by 2 are called odd numbers. In daily life, people usually call positive odd numbers singular, as opposed to even numbers. Odd numbers can be divided into positive and negative odd numbers. The mathematical expression of odd numbers is:

Positive odd numbers: 1, 3, 5, 7, 9,1,13, 15, 17, 19, 2/kloc-. ......

Negative odd numbers:-1, -3, -5, -7, -9,-1,-13,-15,-17,-/kloc. ......